Articulated wheeled vehicles are well known in the form of articulated lorries, where a front portion with an engine pulls a trailer, the front portion also having electrical and brake control over the trailer. Other examples include articulated buses, where a front portion pulls a rear portion. Further, published patent document U.S. Pat. No. 4,762,191 describes an articulated bus with a hybrid drive system, with an IC engine in the front portion and an electric motor in the rear portion.
Articulated tracked vehicles are also known. For instance, published patent document U.S. Pat. No. 5,113,958 describes an articulated tracked snow travel vehicle, whilst published patent document U.S. Pat. No. 5,373,909 describes an articulated tracked vehicle for agricultural harvesting. In the first of these documents, the rear body has an internal combustion engine and drives the complete articulated vehicle. In the second of these two documents, both bodies have hydraulic motors and therefore drive themselves. It is also known to provide an articulated tracked vehicle with an internal combustion engine in the first body for driving the first body, with a driving linkage from the engine to the second body to drive the tracks of that one too.
A single tracked body usually has two track bands, one on each side. Steering of a single bodied vehicle is achieved by causing a traction difference between the two-track bands. During straight driving, the movement of one track band relative to the other is braked. During cornering, traction control is either achieved by applying mechanical friction braking to the inner track band, or by transferring kinetic energy from inner track band to the other by means of a zero shaft (regenerative steering). The latter approach can virtually reverse the movement of one track band relative to the other, when the body is stationary to achieve pivot steer.
However, in the case of an articulated tracked vehicle, steering tends to be achieved differently. Both the above-mentioned document U.S. Pat. Nos. 5,113,958 and 5,373,909, show hydraulic cylinders incorporated into the articulation mechanism between the two bodies. These are controlled to initiate a relative angle between the two bodies (active yaw control), which results in a turn. In wheeled vehicles steering tends not to be so much of a problem where the wheels can pivot. In the case of a four-wheeled rear portion, the front pair tends to pivot with the trailer link. In the case of a two-wheeled rear portion, as in document U.S. Pat. No. 4,762,191, the rear portion is easily turned on just two wheels.